Heretofore proposed electrostatic recording dry toners have been prepared by the method wherein a colorant, a charge controlling agent and other optional additives as magnetic material are combined with a thermoplastic resin, thus obtained mixture is heat-melted and the cooled mass is pulverized and classified to obtain the toner particles of 5 to 15.mu. size.
However, since it is quite difficult to obtain a uniform dispersion of such charge controlling agent as nigrosine, oil black and other dyestuffs, a metal complex of an organic acid and the like in a molten resin, the thus formed toner particles always have the drawback of lacking in uniformity of the amount of charge controlling agent carried on the exposed surface thereof. It is, therefore, unavoidable that when charged, each toner particle acquires each different level of electrical charge, which inevitably causes the failure of exact development of charge pattern made on sensitized material, decrease in transfer ratio and considerable fluctuation in picture qualities at the time of long run continuous reproduction.
Also, since the charge controlling agent covered with the thermoplastic resin and remaining within the toner particle can fulfill only a decreased charge controlling function at the time of electrification, in order to get the toner capable of being electrified at the desired charge, it is essential that an excess amount of expensive charge controlling agent be included within the toner particles, which is economically undesirable.
The inventors, with the object of obviating the aforesaid drawbacks possessed by the heretofore known electrostatic recording dry toners, have continued studies and completed the invention.